Andesite is a crystalline fine-grained igneous rock, extrusive igneous rock composed mainly of plagioclase with other minerals such as hornblende, pyroxene and biotite, occuring mostly in lava flows, but sometimes in dykes and veins. It consists principally of plagioclase felspar, and is often porphyritic, showing large crystals of felspar scattered through a fine-grained mass, usually of small felspar crystals, but often containing much glassy material. Andesite forms most of the recent volcanic rock of the Andes, and is thus named after the Andes.
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